The proposed multi-PI, multidisciplinary investigations will address the fundamental basis of diet-induced obesity (DIO) that currently afflicts one third of adult Americans and is projected to affect >90% of Americans by 2050. While genetics play a role, non-genetic factors introduced through changes in Western diet and lifestyle are the more likely causes for the alarming trends in human obesity. Recently, the role of the gut microbiome in mediating DIO has been suggested, a notion supported by our own preliminary data that show germ-free (GF) mice are protected from DIO and that dysbiosis induced by a high saturated fat diet disrupts the circadian clock (CC) networks of the suprachiasmatic nucleus (SCN) and liver. Circadian rhythms are essential to all life forms, whether human, a member of the animal kingdom, plant, or microbe. Circadian rhythms are endogenous and provide living organisms with the ability to entrain to external cues (zeitgebers) so that they can adapt to, and synchronize with, changes in the environment. We will test the hypothesis that the obesogenic effects of high saturated fat western diets are due to their effects on the chronobiology and function of the gut microbiota, resulting in the generation of specific microbial metabolites that perturb hepatic CC/NR regulatory networks and skew energy states towards the development of obesity. A collaborative approach will be undertaken that includes investigators from The University of Chicago and Emory University who have broad and extensive expertise in research of disease pathophysiology and state-of-the-art analytics for gut microbial metagenomic sequencing, metabolomics, nutritional studies, and relevant bioinformatics. Three specific aims are proposed: (1) to determine if the obesogenic effects of high saturated fat diets are due to their impact on gut microbial chronobiology, function, and metabolomes that specifically target hepatic and central CC regulatory networks, (2) Characterize mechanisms by which gut microbes provide feedback effects on the circadian system in the CNS and liver using classical chronobiological approaches in GF, CONV, and SPF mice. and (3) to identify specific microbe- dependent metabolites from the metabolome that mediate the effects of diet-induced regulation of hepatic CC gene networks and/or their downstream effector pathways using high throughput, hepatic organoid assay systems. Their effects in vivo on hepatic regulatory networks and metabolic/physiological functions will then be vetted in studies involving conventionalized (CONV) and GF mice. Collectively, these data will provide a wealth of novel and clinically-useful information to better understand the role, mechanisms, and mediators of western diet-induced gut dysbiosis in human obesity. This information will have direct relevance to the development of effective therapeutic compounds that can correct the imbalances in brain and hepatic regulatory networks caused by western-diet induced dysbiosis, thereby restoring host metabolic states to health.